I taught high school and ran into the same issue. Stand in the doorway with a bucket; as each student walks in the room, have them put their phones, etc in the bucket. Do not let anyone in your classroom unless they do this. Your next step is to 'shot a hostage' so to speak. You need to show your authority right away. So the next time someone acts up. Kick that person out of your class - permanently. Tell the class from that point forward this is the policy. And of course follow up with the same action if someone else acts up, speaks out, or does whatever you don't approve of in your classroom.
You can't make them learn or enjoy it. But you can weed out the troublemakers.

I had a group of about 6 boys that did the same thing. I gave them an assignment to do a presentation. All six of them played dumb, similar to what you described. So I told the entire class that those 6 just failed the class. Not the assignment. And told them to never come back. From that point on - all the kids straightened up.

"40 students oral communication class in Chinese vocational college" is a madness. So, my idea is to ask for a split of the class or a split with the employer.

I have some big problems with my English oral communications classes here in Guangzhou, China. First off, I have around 40 students per class (freshmen in a vocational college). I'm the only foreign teacher here. Secondly, the classroom is long and narrow, seating perhaps 200. Students sit next to each other, in rows, facing me.
Anyway, that should sound pretty bad already but it's worse than just those logistical problems. About one-third of the class is great- they're responsive and really seem to enjoy English. They sit in front. Then there is a 'no man's land' in the middle where nobody sits. In the back, they are a mixed bunch but at least one-third of the class are doing absolutely nothing. They cannot answer the most remedial of questions and spend their time on WeChat or playing games. They are sullen and even surly sometimes when I tell them to put their phones away. I sometimes get looks like 'what gives you the right to tell me what to do?' when I try to steer them to participate.
You could say, 'just make a seating chart or prohibit sitting behind such and such a row.' I could- but it would backfire. Getting these young adults to even tell us their hobby causes resentment enough, asking them to actually stand up and move causes even more- no, it's not an answer. I can't even play games like the telephone game or a memory game. They sit and debate in Chinese about what they should do and the goal above all seems to be to get away with speaking the least amount of English as possible. I've tried, and still do try, breaking them up into groups. Mostly, while they are supposed to be completing an exercise they're just hanging out, chatting and joking in Chinese. When it's time for presentation, they protest that they don't understand what to do (and folks, we're talking incredibly easy tasks). The fact is that a third of class just doesn't listen to a word I say.
I haven't had classes this bad since I taught in Japan. Any ideas?
I've been teaching in China for five years now and though I've had problems, I've never had students as unmotivated as these.